1. Field of the Invention
The present invention relates to a coin selector in use with various types of service machines such as a vending machine and a coin exchanging machine, and more particularly to a coin selector of the type in which different types of coins are sorted by electronically recognizing the materials or other properties of the coins.
2. Description of the Related Art
An example of the conventional coin selectors of the type which electronically sorts coins is disclosed in U.S. Pat. No. 3870137. The coin selector is so arranged that a coil of an oscillator is disposed along one side of a coin path. The coin selector electronically recognizes the type of a coin in accordance with a deviation of an oscillating frequency of the oscillator, which deviation is caused when the coin passes through the coin path. There are so-called cladding coins, such as 10 cent, 25 cent and one dollar coins. The cladding coin is formed by laminating thin layers of different materials. The cladding coins cannot be detected by using a single oscillator generating a signal of a single frequency. As is well known, when a magnetic field is applied to a coin, magnetic fluxes in a magnetic field alternating at a low frequency penetrates deeply into the coin, while magnetic fluxes in a magnetic field alternating at a high frequency act only in the surface region of the coin. Accordingly, a coin selector whose oscillator oscillates at a frequency so selected as to detect the material of the inner portion of a coin, cannot detect the material of the surface of the coin. To the contrary, a coin selector whose oscillator oscillates at a frequency so selected as to detect the material of the surface of a coin, cannot detect the material of the inner portion of the coin. To cope with this problem, the coin selector disclosed in the U.S. Pat. No. 3870137 uses a plurality of coils arrayed along the coin path, and a plurality of oscillators in connection with the coils. The oscillating frequencies of the oscillators are made different from one another so as to detect the cladding coins. This approach, however, creates another problem that the array of the plurality of coils along the coin path results in an elongation of the coin path, and consequently an increase of a size of the coin selector. The approach has a further problem that the provision of the plurality of oscillators oscillating at different frequencies requires an intricated circuit arrangement.
In the coin selector of the U.S. Pat. No. 3870137, the coin path is inclined by a predetermined angle with respect to a vertical line. This is done to prevent a coin passing through the coin path from moving in a direction transverse to the path so as to maintain a fixed relationship of the coils arrayed on one side of the coin path and the coin passing through the coin path. If the coin path is arranged exactly vertically, distance between a passing coin and the coils changes as the coin moves transversely in the coin path. As the distance between the coin and the coils changes, the deviation of the oscillating frequency of the oscillator changes. Therefore, the coin selector mistakenly recognizes the types of the passing coin. However, the inclined arrangement of the coin path creates another problem. In the arrangement, a coin slides along one side wall of the coin path. When the coin is wet, it tends to jam in the path. Further, in the arrangement, dusty materials tend to deposit on the side wall of the path. When dust is deposited to a certain thickness on the sidewall, a magnetic coupling between a coin and each coil changes. Therefore, a coin sliding down the dusty side wall provides an output signal different from the output signal when the same coin slides down on a clean side wall of the coin path. This degrades an accuracy of the coin selection of the coin selector, and possibly causes frequent improper operations of the coin selector. Further, the inclined arrangement of the coin path requires a larger space. This leads to an increased size of the coin selector.